Those problems were recorded by Brian Dean, he's now a prof at Clemson University http://www.cs.clemson.edu/~bcdean/ He's a fantastic teacher and actually made good use of his tablet pc to help with teaching. If he didn't have time to finish a proof in class, he would email us a flash movie recording of the full proof and he also graded our homeworks in the same way. We'd get back a flash movie containing our typeset submission and he'd comment on each solution and sketch out any improvements or fixes. It was really fun to get feedback like that.